The present invention relates to wood that is reinforced with a fiber-reinforced thermoplastic composite.
As a result of dwindling stocks of high quality lumber, wood product engineers have had to adopt innovative designs to enhance the structural properties and reduce the cost of wood products. Examples of these designs include glue laminated wood beams, laminated veneer lumber, parallel strand lumber laminated wood columns, wood I-beams, and wood trusses. However, merely redesigning the lumber products has not proved adequate. Therefore, efforts have continued to combine low quality, low cost lumber with structurally reinforcing composites to achieve the same performance as achieved with higher cost, higher quality wood products.
For example, O""Brien in U.S. Pat. No. 5,026,593 discloses the use of a thin flat aluminum strip to reinforce a laminated beam. O""Brien teaches that the aluminum strip must be continuous across the width and length of the beam and that the reinforcing strip may be affixed to the lowermost lamina to improve tensile strength or to the uppermost lamina to improve compression strength of the beam.
In U.S. Pat. No. 5,362,545, Tingley (hereinafter xe2x80x9cTingley ""545xe2x80x9d) discloses the use of reinforced plastics in glue laminated wood beams (glulams). More particularly, Tingley ""545 discloses the use of pultruded composites as materials. These composites are prepared by impregnating thermoset or thermoplastic resins into a continuous fiber bundle. The disclosed thermoset resins include epoxy resins, polyesters, vinyl esters, phenolic resins, polyimides, and polystyrylpyridine while the thermoplastic resins include polyethylene terephthalate and nylon-66. The preferred fibers are disclosed as being aramid or carbon fibers or high modulus polyethylene fibers. Tingley ""545 discloses that it is necessary to xe2x80x9chair upxe2x80x9d the surface of the fiber-reinforced composite so that fibers protrude, thereby providing a means of adhering the wood to the composite without having to use expensive epoxy adhesives.
In U.S. Pat. No. 5,498,460, Tingley discloses improved adhesion of the fiber-reinforced composite to the wood by creating multiple recesses distributed over the opposed major surfaces of the composite.
In U.S. Pat. No. 5,547,729, Tingley discloses abraded or haired up synthetic tension and compression reinforcements to provide enhanced tensile and compression strength.
In U.S. Pat. No. 5,641,553, Tingley discloses a reinforcing panel comprising a plurality of substantially continuous and parallel synthetic fibers, affixed to at least one cellulose surface material, which improves adhesion of the panel to a wood structure.
In U.S. Pat. No. 5,885,685, Tingley discloses an aramid fiber mat encased in resin along with the fiber-reinforced composite to reduce interlaminar shear failure when nonepoxy resins are used for encasement.
In U.S. Pat. No. 6,037,049, Tingley discloses a composite that comprises two types of fiber strands encased in a resin matrix, a high strength fiber for the central portion of the composite and a lower strength fiber for the edges. The use of lower cost fibers along the edges reduces waste during a planing process.
In each instance, the prior art requires some kind of modification to the surface of the composite to enhance adhesion to the wood member. It would therefore be desirable to prepare a glue-laminated wood structural member that is reinforced with a composite that adhered to wood either with reduced or no adhesive and without surface modification of the composite.
The present invention addresses a problem in the art by providing a reinforced wood structure comprising an a) elongated multilamellar wood member having an uppermost lamina with an outer surface, a lowermost lamina with an outer surface, a longitudinal center, and a transverse center; and b) a first elongated fiber-reinforced thermoplastic composite layer disposed 1) through the longitudinal center of the wood member; and 2) between and adherent to the major surfaces of two of the laminae, or adherent to the outer surface of the uppermost or the lowermost lamina; wherein the composite contains a plurality of substantially parallel continuous fibers impregnated with a thermoplastic polymer having the following structural units: 
where Z is S or O, and Zxe2x80x2 is S, O, N-alkyl or NH.
In a second aspect, the present invention is a reinforced wood structure comprising a) an elongated multilamellar wood member having an uppermost lamina with an outer surface, a lamina adjacent to the uppermost lamina, a lowermost lamina with an outer surface, and a lamina adjacent to the lowermost lamina; b) a first elongated fiber-reinforced thermoplastic composite layer disposed through the length of the wood member and between and adherent to the uppermost lamina and the lamina adjacent to the uppermost lamina; c) a second elongated fiber-reinforced thermoplastic composite layer disposed through the longitudinal center of the wood member and between and adherent to the lowermost lamina and the lamina adjacent to the lowermost lamina, wherein the composite layers each contain a plurality of substantially parallel continuous fibers impregnated with a thermoplastic polyurethane.
In a third aspect, the present invention is a reinforced wood structure comprising a fiber reinforced thermoplastic composite layer disposed onto wood or dispersed into wood particles, wherein the thermoplastic composite layer contains a plurality of substantially parallel continuous fibers impregnated with a thermoplastic polymer having the following structural units: 
where Z is S or O, and Zxe2x80x2 is S, O, N-alkyl or NH.
In a fourth aspect, the present invention is a reinforced wood structure comprising a first fiber-reinforced thermoplastic composite flange and a second fiber-reinforced thermoplastic composite flange, each flange being bonded to a web to form a reinforced I-beam, wherein the fiber-reinforced thermoplastic composite flanges contain a plurality of substantially parallel continuous fibers impregnated with a thermoplastic polymer having the following structural units: 
where Z is S or O, and Zxe2x80x2 is S, O, N-alkyl or NH.
In a fifth aspect, the present invention is a reinforced wood structure comprising an elongated multilamellar wood member having a longitudinal center, a transverse center, a width center, and a plurality of elongated fiber-reinforced thermoplastic composite rods, at least two of which rods are tension reinforcement rods and at least two of which rods are compression reinforcement rods, wherein the tension reinforcement rods are disposed through the longitudinal center, and distal on either side of the width center and imbedded into and adhering to a lamina distal from the transverse center and proximal to the lowermost lamina of the multilamellar structure, and wherein the compression reinforcement rods are disposed through the longitudinal center, and distal from either side of the width center and imbedded into and adhering to a lamina distal from the transverse center and proximal to the uppermost lamina of the multilamellar structure.
In a sixth aspect, the present invention is a reinforced wood structure comprising a wood member having slots or bores and a plurality of elongated fiber-reinforced thermoplastic composite rods incorporated into the slots or bores of the wood member.